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Jack, Technician

Category: Consumer Electronics

Satisfied Customers: 9533

Experience: 35 years experience as audio/video repair and installation tech.

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I want to know if you can help me a little problem I have

Customer Question

Hello!... I want to know if you can help me a little problem I have uncounted…. I have a two-in-one device a volt meter and a amp meter “DROK® Voltmeter Ammeter Volt Amp Multimeter DC 4.5-30V 150A Voltage Current Monitor Ampere Testing Gauge V/A Panel Meter Red/Blue Dual LED with Current Shunt Car Auto Motorcycle Battery Power”.. It’s a digital led display unit volts displayed on top and the amp on the bottom….. Now it has 3 wires one for the dc voltage in also for the voltage display…one for the negative for the device and voltage measurement… and the last wire is used for the amps…. Now the shunt is connected on the load at the negative wire.. Therefore the volt drop for the meter must be from battery negative and 175mv = (150 amps) across the shunt into the third wire…The volts and amps has the negative wire as common… Can you help me connect this work on a car alternator since I can’t isolate the negative of the alternator..

Hello there and welcome to Just Answer. My name is ***** ***** I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.

The case of the alternator is the 'negative'. The alternator grounds through it's connection to the engine block. So you can take the negative off literally ANY ground on the car.

OK so how do I measure the current from the alternator with out having the electrics and the starter motor currents past trough the 150A shunt resistor?....Did you understand the notes and questions posted?...Check out this link : http://ecx.images-amazon.com/images/I/61CUVF%2B%2ByOL._SL1200_.jpg

There is a diagram of the connections.. how do you get the shunt resistor to work on the positive wire and feed the current sense wire with no more than 175mv to ground (-)?

I do not see a reason why you would not put this on the positive side of the circuit. The meter will not experience the starter current - the shunt will but it is designed to. I doubt you would see more than 150A on a starter and even if you did, the shunt will handle much more than that. The instructions for installing on the negative side is a safety concern on the part of Drok. By keeping the shunt at a ground potential, the chance of a short circuit is reduced.

Hello , my name is JackPerhaps I can help you with this problem but first i would have a few questions so could you please send me a reply (if you still need help with this ) when you are ready to proceed ?

Now this will monitor the load and voltage between the alternator and batteries so the current there is very unlikely to go over 150 amps unless you are connecting a welder to charge your batteries .

A heavy duty alternator will put out 90 amps and say that you have an out of the ordinary alternator then perhaps 120 amps coming out at max and again that would be with completely dead batteries and lots of them so I cannot see how you would go above 150 amps =175 MV and if you do then you cannot limit that 175v without getting false readings at the meter , in that case what you would need is a bigger shunt

And also keep in mind that the voltage must swing from 0 - 175mv so I think a circuit may be built to allow the current sense wire to be at zero volts when no current is passing...and what I see if the shunt is on the POS. side of the alt. it would have no less than 12v on the shunt to ground and 175mv is the max into the sense wire..

No it's for DC and that motor is just a representation of the load ( it's chines)..got figure!..

But you can't come up with a something or device to make it work... Now if the black wire was able to be separated and have two wire for currnt and two for volts maybe I mite gen it to work... but it difficult to get 0-175mv from something connected on a live/hot wire...

You use the link and/or phone number i give you and get a refund , that thing will not work unless you are prepared to do some heavy ground rework on your vehicule to isolate the alternator from that chassis and then again would end with heavy static through the audio system .

Just saw your reply and that is cool and very appreciated , that can be worked out as well , use the phone number or link there then and tell them what you think is a fair price